This invention relates to drive devices such as power transmission belts, and more particularly to a drive device in which a ribbed belt has a tension section, a neutral axis section and a compression section. The outer surface of the belt, i.e., the upper surface of the tension section is flat. The compression section, i.e., the inner surface of the belt, has a plurality of ribs arranged longitudinally thereof. Alternatively a banded belt having a plurality of V-belt bodies having a trapezoidal section is arranged in parallel and separately from one another and a tie band of rubberized fabric or rubberized code fabric is laid over the upper surfaces of the V-belt bodies to connect them. The fabric is laid in a serpentine manner over a driving pulley and a plurality of driven pulleys.
Heretofore, in V-belt drive devices for an automobile, V-belts are, in general, laid over a crank pulley, a alternator pulley and a fan pulley, over a crank pulley and a power steering pulley, and over a crank pulley and a cooler pulley, respectively. That is, several belts are used in one automobile.
However, a device in which only one ribbed belt is laid in a serpentine manner over such pulleys to drive the latter has been proposed and is being put into actual use (See: U.S. Pat. Nos. 3,951,006, 4,031,761 and 4,028,955).
This conventional drive device utilizes the technological merits of a ribbed belt which is thin and flexible. In the drive device, the outer surface or the inner surface of one ribbed belt are selectively brought into contact with a crank pulley, a fan pulley, a power steering pulley, an alternator pulley, a cooler pulley, etc., and an idler pulley is provided to give a predetermined tension to the belt. That is, the ribbed belt is laid in a serpentine manner over these pulleys. Among these pulleys, at least one pulley, for instance the fan pulley, is a flat pulley which is driven by the outer surface of the belt.
The drive device of this type is advantageous over the drive device in which several belts are laid over pulleys in the following respects:
(1) Since the width of the pulleys can be reduced, the space in the automobile can be effectively utilized, and the weight of the automobile can be reduced.
(2) Since the ribbed belt is more flexible than a V-belt, the amount of energy consumed for driving the belt can be reduced, and accordingly, fuel consumption is reduced.
(3) Since the tension of the belt is adjusted by the idler pulley, fluctuation of the belt tension is less, and therefore the belt is not susceptible to breakage.
(4) Since only one belt is laid over the pulleys, if the belt is broken, it can be readily replaced with a new one.
However, the disadvantage of this conventional drive device resides in the use of the flat pulley. Since the flat pulley has no pulley groove, the belt is liable to transversely shift on the pulley, which may non-uniformly wear the belt and cause abnormal sounds.
The rib thickness of the ribbed belt is about or less than half of the thickness of the V-belt. Therefore, if the belt is vibrated, then the ribs of the belt are disengaged from the grooves of the pulley. Therefore the belt is transversely shifted on the pulley and in a worst case, it may come off the pulley.